Delivery of interactive content with broadcast programming presents several special issues. First, for the interactive content to be effective, it should be synchronized with the broadcast. This entails delivering an interactive complement to an advertisement at the same time that the broadcast advertisement airs, or coordinating interactivity with events in the ad.
Second, the delivery of interactive content should be reliable. Since the interactive content is broadcast in a data stream parallel to the video stream, there is the possibility that the interactive content might be stripped out or corrupted at the broadcast site, or at the local subsystem, such as a local network affiliate or a cable headend. Finally, it is often desirable to target the interactive content to the specific viewer or delivery system. Digital cable systems, for example, have much higher bandwidth for delivering interactive content than the limited bandwidth provided by the vertical blanking interval (VBI) data transmission methods available to analog cable systems. It is advantageous to build a system that selectively utilizes this higher bandwidth when present in the broadcast environment. Additionally, demographic factors might motivate targeting different interactive content to different delivery systems.